Connecting a known and unknown battery

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In summary, the conversation discusses the determination of emf and internal resistance of an unknown battery by connecting it to a known battery in two different configurations. The equations and solution for finding the emf and resistance are provided, with confirmation that the answer is correct and clarification on the connection of the batteries.
  • #1
mike115
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[SOLVED] Connecting a known and unknown battery

Homework Statement


An unmarked battery has an unknown internal resistance. If the battery is connected to a fresh 5.60 V battery (negligible internal resistance) positive to positive and negative to negative, the current through the circuit is 10.0 mA. If the polarity of the unknown battery is reversed, the current increases to 25.0 mA. Determine the emf and internal resistance of the unknown battery. Assume that in each case the direction of the current is negative to positive within the 5.60 V battery.


Homework Equations




The Attempt at a Solution


I tried making two equations using the loop rule for each setup.

5.6 - .01*r - e = 0
5.6 - .025*r + e = 0

e = 2.4 V
r = 320 ohms

Would that be right? The resistance looks a little too high to me.

When it says the batteries are connected positive to positive, does that mean the batteries are connected in series in the circuit?
 
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  • #2
mike115 said:
e = 2.4 V
r = 320 ohms

Would that be right? The resistance looks a little too high to me.

When it says the batteries are connected positive to positive, does that mean the batteries are connected in series in the circuit?

The answer is right. Positive to positive just means that the positive sides are connected to each other.

This has nothing to do with being in series, because the batteries will be in series no matter how you connect them.
 
  • #3
All right, thanks kamerling!
 

1. How do I determine the polarity of a known battery?

The polarity of a battery can usually be determined by looking at the markings on the battery. The positive end will typically have a plus sign (+) or the word "positive" written on it, while the negative end will have a minus sign (-) or the word "negative" written on it.

2. Can I connect a known battery to an unknown battery?

Yes, it is possible to connect a known battery to an unknown battery. However, it is important to make sure that the polarity of the batteries is matched correctly to avoid damaging the batteries or any connected devices.

3. What is the safest way to connect a known and unknown battery?

The safest way to connect a known and unknown battery is to use a battery holder or terminal block. These devices provide a secure and controlled way to connect the batteries, ensuring that the polarity is correct and minimizing the risk of short circuits or other potential hazards.

4. Can I connect batteries of different voltages together?

It is not recommended to connect batteries of different voltages together. This can cause an imbalance in the circuit and potentially damage the batteries or any connected devices. It is best to use batteries of the same voltage when connecting them together.

5. What should I do if I accidentally connect a known and unknown battery with the wrong polarity?

If you accidentally connect a known and unknown battery with the wrong polarity, there is a risk of short circuiting the batteries or any connected devices. It is important to disconnect the batteries immediately and check for any damage before attempting to reconnect them with the correct polarity.

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